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2017-21

Although the historic preservation community subscribes widely to the notion that historic buildings contain “inherent energy efficient features” as part of their traditional construction, there is no consensus about how to quantitatively identify and evaluate the benefits of such features.  To date, inherent energy efficient features – such as operable windows, interior or exterior shading, and thermal mass – have been identified and discussed primarily in qualitative terms.  This is a major limitation, given that decisions about energy retrofits in buildings are typically made on the basis of quantitative metrics, such as estimated energy savings and economic payback.

Sponsored by the National Center for Technology and Training, Dr. Amanda Webb, Assistant Professor of Architectural Engineering at the University of Cincinnati, and Dr. Thomas Boothby of the Penn State University have  developed a new method for quantifying the benefits of inherent energy efficient features using building energy simulation and sensitivity analysis.

The procedure involves simulating the effects of qualitatively identified inherent energy efficient features along with other proposed energy retrofits on building energy consumption.  Based on data obtained from the building, a model is developed to predict the response of the building to outdoor temperature, solar gain, internal loads and other factors.  This model can be calibrated to the actual performance of the building.

Following the development of a calibrated model of the thermal performance of the building, a series of potential modifications to the building are chosen.  As this project involves looking at preservation-sensitive measures, most of the options investigated have the characteristic of being less intrusive on the character of the building.  The model is run with random combinations of these energy conserving measures, and with variable exterior environments and internal loads, calibrated to the actual thermal environment of the building.  Each run is identified as ‘behavioral,’ meaning that it meets an expectation of saving 50% of the energy used in the present form of the building, or ‘non-behavioral. ‘

Historic view of a stone and brick building with attached greenhouse

Old Botany building from the southeast, c. 1889

The result of these runs is a list of combinations of strategies that are expected to result in the desired 50% energy savings.  While single measures alone cannot achieve the desired outcome, a number of combinations are expected to have a positive outcome.  The designers of the retrofit have the option of choosing which group of these measurements is least likely to impact the historic character of a property.  In the case of the study of Penn State’s Old Botany Building, it was noted that the performance of the building is heating-dominated, that is measures that impact cooling loads, such as thermal shading, landscaping, low-E glass, etc. had very little effect on the energy consumption of the building.  As a result of this, combinations of attic insulation, wall insulation, and reducing infiltration were discovered to have the greatest positive effect on the energy usage of the building.  Within these findings, it was possible to increase the amount of insulation and to use a lower standard on air infiltration, if this is desired by the designers.

The findings and method of this project make it possible to take the dialogue about energy retrofits to historic buildings beyond the simple consideration of inherent energy efficient features, and to consider the whole performance of the building in the light of the feasible measures that can be taken, and for the designers of the retrofit to be able to choose among several packages of measures, the one that goes the farthest to meet the joint objectives of energy conservation and historic preservation.

National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119